The structures and conformations of the following physiologically active compounds will be determined by single crystal X-ray techniques: rotenone or its p-bromophenyl-hydrazone, the p-bromobenzoate of piericidin A, the bromosalicylate of genersine, the hydrobromide of physostigmine, dimethan, pyrolan, the bromophenylhydrazone of pyrethrin I, the benzyl-3-furylmethylester of chrysanthemum acid, quassin, zearalenone or its bromophenylhydrazone, the potassium salt of the Schiff base of pyridoxal and D,L-alanine, chloramphenicol, clavicipitic acid, malemycin, and tetrahydroisoanemonin. The nmr spectra of rotenone, piericidin A, zearalenone, quassin, and chloramphenicol will be measured or remeasured and the coupling constants interpreted, if possible, in terms of the conformation of the compound in the solid state. Where possible, the nmr spectra of the above compounds will be measured in solutions approximating physiological conditions. These studies will hopefully solve one or more of the following biologically important problems: (1) the elucidation of the structure of physiologically important compounds; (2) the determination of the physiologically active conformation of these compounds, which will hopefully provide insight into the mechanism of action of these agents, the conformation of their binding sites on enzymes, and their structure-activity relationships; and (3) the comparison of the conformation of these compounds in the solid state and in solution. This comparison should provide important and perhaps exciting knowledge concerning the relationship between the conformations of these compounds in the solid state and in solution.